FILE - This is an undated picture displayed on a missing poster shows 8-year old Sandra Cantu from Tracy, Calif. Melissa Huckaby, 29, a California Sunday school teacher accused of kidnapping, raping and killing Cantu, an 8-year-old playmate of her daughter, then stuffing her body in a suitcase, pleaded guilty Monday, May 10, 2010 to murder.

Photo: Jose Carlos Fajardo, AP

FILE - This is an undated picture displayed on a missing poster...

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FILE - In this April 14, 2009 photo, Melissa Huckaby, 28, is shown in a Stockton, Calif., courtroom during her arraignment. Huckaby has pleaded guilty to killing her daughter's playmate, Sandra Cantu, last year. A gag order has been in place in the case preventing court records from being unsealed. Several news organizations, including The Associated Press, are expected to argue in a Stockton court on Monday, May 24, 2010, that information on the case be made public.

Photo: Paul Sakuma, AP

FILE - In this April 14, 2009 photo, Melissa Huckaby, 28, is shown...

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Melissa Huckaby, 29, of Tracy, Calif. wipes her eyes as she reads a statement apologizing to the family of Sandra Cantu, her own family, her daughter, the city of Tracy and others before being sentenced in the San Joaquin County Courthouse in Stockton, Calif. on Monday, June 14, 2010. The Sunday school teacher who pleaded guilty to kidnapping and murdering Sandra Cantu, an 8-year-old neighbor girl in Northern California, made a tearful apology to the victim's family Monday as she was sentenced to prison for the rest of her life.

Photo: Cindi Christie, AP

Melissa Huckaby, 29, of Tracy, Calif. wipes her eyes as she reads a...

A former Sunday school teacher was sentenced Monday to life in prison without parole after she tearfully apologized and begged for forgiveness for murdering 8-year-old Sandra Cantu in Tracy, saying the girl "did not suffer."

Melissa Huckaby said she still struggles for an explanation for why she killed Sandra. She said she believes God has forgiven her, and she asked for the same forgiveness from Sandra's mother, Maria Chavez.

"I still cannot understand why I did what I did," Huckaby, 29, said in a packed Stockton courtroom as relatives of Sandra and Huckaby wept in the gallery.

"It is not enough that I say I'm sorry, but that is all I can do," Huckaby said. She said she will have to live with her decision to kill a "sweet and innocent" little girl for the rest of her life.

She said Sandra did not suffer and added, "I did not sexually molest your daughter."

But at a news conference after the hearing, Deputy District Attorney Tom Testa said, "I found that statement strange, and I don't think a jury would have accepted it. It's hard for me to believe that Sandra Cantu did not suffer."

Plea bargain

Prosecutors initially charged Huckaby with a number of sex crimes, but those counts were dropped in exchange for her guilty plea May 10 to first-degree murder and the special circumstance of kidnapping. Prosecutors also agreed not to seek the death penalty.

Although Huckaby's motives may never be known, San Joaquin County prosecutors revealed Monday how she killed Sandra - by asphyxiating her with a torn cloth drenched with rubbing alcohol.

Sandra's body was found April 6, 2009, stuffed in a suitcase in a dairy farm's irrigation pond 2 miles from her home at the Orchard Estates Mobile Home Park in Tracy, where both the girl and Huckaby lived.

Authorities said the blood-stained piece of torn cloth had been tied around Sandra's head and knotted into a noose. Traces of alprazolam, a sedative, were found in her system, the same medication found in Huckaby's purse and home, they said.

'Practice attempts'

Testa said Huckaby had used the same drug to knock out a 7-year-old girl in January 2009, and Daniel Plowman, a former boyfriend of Huckaby's who was sickened 25 days before Sandra was killed. Prosecutors dropped charges in those cases as part of the plea bargain with Huckaby.

Investigators believe the two earlier druggings may have been "practice attempts" leading up to Sandra's slaying, Tracy police Detective Timothy Bauer said.

Sandra suffered injuries to her genitalia that were consistent with the diameter of the handles of a rolling pin that was found at the nearby Clover Road Baptist Church, where Huckaby taught Sunday school and where her grandfather is the pastor. The rolling pin had a "bloody smudge" on it, and its handle was bent, authorities said.

The blood contained Sandra's DNA, authorities said.

Sandra was killed only moments after a surveillance video captured images of her skipping near her home March 27, 2009, prosecutors believe.

On the video, as the girl is skipping, "something catches her eye, and she looks over in the direction of Melissa Huckaby's residence," Testa said. Huckaby is the mother of one of Sandra's playmates.

The same video shows Huckaby's sport utility vehicle leaving the mobile home park eight minutes later and going to the church down the road. Huckaby phoned the trailer park manager from the church to report that her Eddie Bauer suitcase had been stolen from in front of her home.

Her actions showed that she was "lucid" and that "her mind was working that night," Testa said.

About 85 minutes after the phone call, the surveillance video shows Huckaby driving away from the church, authorities said. She was gone for about a half hour.

Spotted at pond

"It is during that 30-minute period that both a retired U.S. Marine and his wife see Melissa Huckaby and her SUV at an irrigation pond at Bacchetti Road and Whitehall Road in Tracy," Testa said in a statement summarizing investigators' findings. "Melissa tells them she was there to urinate."

The next day, Huckaby showed police a handwritten note that she said she had found in the trailer park. The note, riddled with misspellings, read, "Cantu locked in stolin suitcase thrown in water on Bacchetti Rd. & Whitehall Rd witness."

"The handwriting, though disguised, has similarities to Melissa Huckaby's known handwriting," Testa's statement said.

Sandra's body was found in an Eddie Bauer suitcase in the same pond where the retired Marine and his wife had seen Huckaby, authorities said.

Huckaby was arrested four days after the girl's body was found.

Relatives speak

In court Monday, Sandra's aunt, Angie Chavez, played a DVD showing pictures of Sandra as she was growing up. Many in the gallery wept.

Sandra's grandmother Connie Cantu and father, Daniel Cantu, said in court that they also felt sorry for Huckaby's young daughter. Choking back tears, Daniel Cantu told Huckaby, "You took the life of an innocent little girl."

Judy Lawless, Huckaby's mother, also addressed the court, saying she and her family have grieved and prayed for Sandra's family.

"If I could take this all away, I could, but I can't," Lawless said. "I know these are words, but they're words from the heart. From mother to mother, I'm so sorry."

Huckaby had been undergoing mental evaluation as a result of an earlier petty-theft conviction, and relatives said she had battled depression. Sources said she tried to commit suicide in the days before her arrest by swallowing razor blades.